This invention relates to a rotating electrical machine and more particularly to an improved method for securing the permanent magnets to the carrier thereof in such a machine.
In many types of rotating electrical machines, there are provided a plurality of circumferentially spaced permanent magnets that cooperate with coil windings so as to either effect rotation of an output shaft, if the machine is a motor, or to output an electrical current, if the machine is a generator. Frequently, though not always, these permanents magnets are formed on the stator or yoke of the machine. Regardless of whether the permanent magnets are fixed or rotate, there is a problem with the prior art method by which they have been assembled.
Generally the permanent magnets have been bonded with an adhesive to a circumferential surface of a carrier before the permanent magnet material has been magnetized. Then, the segments are magnetized to give alternating polarities utilizing a magnetizer.
It has been the practice to apply the permanent magnet material to the carrier by utilizing an adhesive between the magnetic material and the carrier surface. The adhesive is secured in place by applying pressure to the two members with the adhesive being applied to one or both of these surfaces to be joined.
Since gaps are left between the adjacent magnets, the adhesive tends to be forced out of the gap between the two members. This is generally not a problem when using ferromagnetic materials because they have considerable thickness. However, the use of said thick magnets has several disadvantages in that it increases the size of the machine and also decreases its efficiency.
It has therefore, been proposed to use high magnetic flux density materials such as neodymium-iron-boron materials and the like. By utilizing this type of material having a high flux density, the thickness of the permanent magnet can be considerably smaller to reduce the size of the motor and to increase its efficiency.
The advantage of the thinness of the material, however, presents a problem in connection with adhesive bonding. That is, it significantly increases the likelihood that the adhesive material may be forced outwardly from beyond the edges of the adjacent magnets and protrude beyond them. In such a case, the raised adhesive is likely to contact the coils with which the magnets cooperate or their armatures. When such contact occurs, there is a likelihood that the magnets may become separated and/or the magnets or the coils become damaged.
It Is, therefore, a principal object to this invention to provide an improved method and improved structure by which permanent magnets are mounted that permits the use of adhesive bonding and thin magnets without the likelihood that the adhesive will protrude beyond the magnet surfaces.
Also, it is a further object to this invention to provide an improved method for adhesively bonding permanent magnets to a carrier.
A first feature of the invention is adapted to be embodied in an electrical machine having permanent magnets. The machine is comprised of a carrier having a cylindrical surface portion and a plurality of permanent magnets each having a cylinder surface complimentary to and spaced at circumferentially spaced locations from the carrier cylindrical surface portion. At least one circumferential groove is formed in one of the carrier and the plurality of magnets contiguous to the cylindrical surface portion. An adhesive bonds the permanent magnets to the cylindrical surface portion of the carrier and is supplied from the circumferential groove to the area between the cylindrical surface portion of the carrier and the cylindrical surfaces of the permanent magnets.
Another feature of the invention is adapted to be embodied in a method of making the rotating electrical machine as set forth in the preceding paragraph wherein the cylindrical surfaces of the permanent magnets are held in spaced relationship to the carrier cylindrical surface portion and an adhesive is supplied to the circumferential groove and permitted to fill the area between the cylindrical surfaces of the permanent magnets and the cylindrical surface portion of the carrier.